This invention relates to packaging, and more particularly to a method of and apparatus for wrapping products in flexible sheet material in which a continuous web of such material is formed into a tube, and transverse seals are formed across the tube at package length intervals with a unit of the product to be packaged between successive seals.
The invention may be regarded as involving improvements on the method and apparatus disclosed in the U.S. Pat. No. 3,274,746 of Robert C. James, David A. Wilson and Frank E. Pringle, Jr., issued Sept. 27, 1966. In the method and apparatus of this patent, a web of flexible sheet material is continuously fed forward and formed into a tube with an inside-face-to-inside-face longitudinal seam. Units to be packaged, e.g., units of cheese, feed forward on the web, spaced at intervals corresponding to the desired package length, the web being formed into a tube around the units. Transverse seals are formed across the web at package length intervals between units by a rotary transverse sealer of the type disclosed in U.S. Pat. No. 2,976,657 issued Mar. 28, 1961, the resultant packages being severed at the seals. The web with the units thereon travels under a hood or manifold for supplying to the tube of packaging material a gas, e.g., carbon dioxide, for preservation of the units in the packages. Side portions of the web are folded up at opposite sides of the manifold and the side margins of the web are brought together in inside-face-to-inside-face relation at the apex of the former. They then pass between a pair of heater bars (indicated at 22 in U.S. Pat. No. 3,274,746) for heating them, and then are pressed together by means of a pair of pressure rolls to form the longitudinal seam.
A problem has occurred in certain instances of use of the apparatus shown in U.S. Pat. No. 3,274,746 to package products in certain types of flexible packaging material which have a coating of heat-sealable plastic on one face of a non-heat-sealable substrate. In such case, the heat must penetrate the substrate to reach and soften the heat-sealable face of the material, and in some instances the degree of heat required to penetrate the substrate for this purpose may be so high as to damage the substrate. This method reduces the speed potential of the equipment because of the time taken for the heat to penetrate the substrate. Another problem that has occurred in certain instances of use of said apparatus has been that of relatively high gas consumption.